Jack using flexible expansible motor

ABSTRACT

A portable jack using an expansible motor having a flexible wall wherein the jack consists of a frame mounted upon wheels. A casing or assembly is mounted upon the underside of the frame intermediate the frame and the floor, and houses the expansible motor which is supplied with a pressurized medium through a hose or the like. Pressurization of the expansible motor causes a lower portion of the casing or assembly to extend downwardly to engage the floor and raise the frame relative thereto. The expansible motor operation may utilize both hydraulic fluid and compressed air, and a pair of expansible motors may be utilized in parallel to increase the jack lifting capacity.

United States Patent Hollerith 3,751,007 Aug. 7, 1973 JACK USING FLEXIBLE EXPANSIBLE MOTOR Inventor: Charles Hollerith, 715 W. Michigan Ave., Jackson, Mich.

Filed: Dec. 27, 1971 Appl. No.: 211,908

US. Cl. 254/2 R, 254/93 R int. Cl. B60p l/60, B66f 3/24, B66f 5/04 Field of Search 254/2 R, 2 BC, 93 HP References Cited UNITED STATES PATENTS Primary Examiner-Othell M. Simpson Attorney Beaman & Beaman 57 ABSTRACT A portable jack using an expansible motor having a flexible wall wherein the jack consists of a frame mounted upon wheels. A casing or assembly is mounted upon the underside of the frame intermediate the frame and the floor, and houses the expansible motor which is supplied with a pressurized medium through a hose or the like. Pressurization of the expansible motor causes a lower portion of the casing or assembly to extend downwardly to engage the floor and raise the frame relative thereto. The expansible motor operation may utilize both hydraulic fluid and compressed air, and a pair of expansible motors may be utilized in parallel to increase the jack lifting capacity.

10 Claims, 7 Drawing Figures PATENIED 3.751.007

sum 1 or 3 44 P i 32 2% i g; 66

-FZG. 4 5.; I INVENTOR CHARLES HOLLERITH ATTORNEYS PATENHU SHHI 2 BF 3 76 EF'JG. 3

INVENTOR ARLES HOLL ITH B MAJ ATTORNEYS l JACK USING FLEXIBLE EXPANSIBLE MOTOR BACKGROUND OF THE INVENTION The invention pertains to a portable jack utilizing compressed air or a hydraulic fluid to produce the lifting action.

While portable jacks using hydraulic liquid, or compressed air expansible motors, are known, a number of applications that require the use of jacks do not readily lend themselves to available constructions. For instance, in the handling of large boats it is common practice to place the boat upon a cradle which is supported on wheeled dollies and the cradled boat is then moved to a desired storage location. Thereupon, the cradle is lifted from the wheeled dollies by jacks and blocks are placed under the cradle so that the jacks can be removed. Jacks available for this purpose are troublesome to handle and use, and the boat cradle cannot be uniformly lifted unless at least four operators are available.

Boat jacks, and other types of jacks which may be used with large, heavy and bulky items must have a low profile in order to permit use in locations having limited vertical clearance. However, it is necessary that such jacks have a large lifting capacity, even through the height of lift required is not great. Additionally, it is important that the jack not be susceptible to tipping or undesired displacement due to lateral forces that may be imposed upon the jack while extended.

The jack of the invention is considered to be an improvement over portable jack devices using expansible motors such as shown in U.S. Pat. Nos. 2,070,960 and 3,010,698. The type of jack shown in these patents shows a wheeled support wherein the load is supported upon the wheels at all stages of operation of the expensible motor. This type of construction is not suitable in those applications wherein a greater stability is required during load movement than is possible with an extended jack mounted upon wheels. In the invention the extension of the expansible motor disengages the frame ground wheels with the floor and a very stable lifting action is accomplished.

SUMMARY OF THE INVENTION It is a basic object of the invention to provide a portable jack utilizing an expansible motor wherein the jack is of a rugged, relatively inexpensive construction, capable of exerting high lifting capacities, is of a low profile, and produces unusually stable characteristics during extension.

In the practice of the invention a frame is utilized which is mounted upon at least three ground wheels wherein the frame may be easily rolled from one location to another. The overall height of the frame is low, most models being of less than one foot high, and a casing or assembly is mounted upon the underside of the frame which houses the expansible motor. The casing or assembly includes an upper portion fixed relative to the frame and a lower portion movably mounted on the upper portion which is movable toward and away from the frame and, upon extension, will engage the floor uponwhich the frame is located. The lower casing or assembly portion is capable of sufficient extension to engage the floor and raise the frame from its normal position wherein the frame supporting wheels are lifted from the floor and the weight of the load and the jack are removed from the frame wheels.

Stop means associated with the casing or assembly limit the degree of extension of the lower portion, and springs are preferably interposed between the casing or assembly portions for retracting the lower portion upon the release of the pressure within the expansible motor.

The expansible motor, preferably, is in the form of a flexible wall chamber, and either compressed air or pressurized hydraulic fluid may be used to expand the motor. In one embodiment of the invention a fluid reservoir is located in the casing, and the presence of compressed air within the fluid reservoir will cause a flow of hydraulic liquid from the reservoir into the expansible motor through a control orifice regulating the rate of motor expansion, and in-this manner the use of fluid substantially minimizes the amount of compressed air necessary to extend the jack.

In other embodiments of the invention a plurality of flexible wall chambers are mounted in parallel wherein a relatively inexpensive, high capacity, quick acting, expansible motor jack construction is achieved.

It is therefore an object of the invention to provide a portable jack utilizing an expansible motor, preferably of the flexible walled type, wherein the jack is capable of quickly lifting heavy loads, may be economically manufactured, assembled and maintained, and produces. unusual stability of the load when extended.

BREIF DESCRIPTION OF THE DRAWINGS The aforementioned objects and advantages of the invention will be apparent from the following description and accompanying drawings wherein:

FIG. 1 is a perspective view of a portable jack constructed in accord with the invention,

FIG. 2 is an elevational view of the jack of FIG. 1,

FIG. 3 is an enlarged, detail, partially sectioned, diametrical view of the casing and expansible motor of the embodiment shown in FIGS. 1 and 2,

FIG. 4 is an enlarged, detail, sectional view of the pressurized medium inlet passage taken along Section IV-IV of FIG. 3,

FIG. 5 is a diametrical, sectional view of an embodiment of the invention wherein a plurality of expansible motors are connected in parallel, and

FIGS. 6 and 7 are diamctrical, sectional views of another embodiment of the invention using two motors mounted on a common assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A portable jack utilizing the structural concepts of the invention may be constructed in a wide variety of embodiments. A basic embodiment of the invention is shown in FIGS. 1 through 4, and in this embodiment the portable jack includes a plate 10 which constitutes the basic frame component. The plate 10 may be of a generally triangular configuration, and includes an upper side 12, and an underside 14.

The plate 10 is supported by ground wheels 16, three being shown in the disclosed embodiment. The ground wheels are preferably in the form of heavy duty casters mounted upon yokes 18 which depend from thrust bearings 20 attached to the frame 10 by thrust plates 22 affixed to the frame by bolts 24, or may be welded thereto. The caster wheels are of the type capable of swinging in a horizontal plane through 360 of rotation, and in this manner the frame may be readily guided across the floor or other supporting surface.

A casing or assembly generally indicated at 26 is mounted to the underside of the frame by bolts 27, FIG. 2. The casing 26 is preferably ofa generally circular configuration and includes an upper portion 28 and a lower portion 30. The casing upper portion 28 is of a hollow configuration, FIG. 3, defining a chamber 32 between the cover plate 11 and a bottom wall 34 which may function as a reservoir. A cylindrical downwardly extending wall 36 is included in the configuration of the casing upper portion and this configuration forms a guide for the lower casing portion 30.

The lower casing portion 30 is also of a cylindrical configuration and is preferably of a dished shape such that the axial portion 38 is slidably, telescopically guided over the casing wall 36. A radially extending annular flange 40 is defined on the outer configuration of the lower casing portion and a plurality of bolts 42 threaded into threaded holes 44 defined in the upper casing portion 28 extend through holes 46 defined in the flange wherein the bolt heads serve as stops to limit the downward extension of the lower portion 30 relative to the upper casing portion. The bolt heads 48 engage the underside of the flange 40 upon full extension of the lower casing portion, and lock nuts 50 are utilized to secure the desired adjustment of the stop bolts 42.

Retraction of the casing lower portion 30 is achieved by a plurality of tension springs 52 disposed about the periphery of the casing having an upper end attached to casing portion 28 adjacent the cover plate 11, and the lower end attached to the flange 40. As will be apparent in FIG. 3, the preferred means for attaching the springs to their associated components is to provide a hole 54 in the casing upper portion, through which the end of the spring extends, a recessed portion 56 is defined adjacent the frame plate and a pin 58 of a length greater than the diameter of hole 54 and less than the diameter of recess 56 is inserted through the eye of the spring to anchor thespring relative to the frame plate. In a like manner, the flange 40 is provided with a hole 60 for receiving the spring and a larger hole provides the recess into which the spring anchor pin 62 is received.

In the preferred embodiment of the invention the chamber 32 constitutes a reservoir adapted to be partially filled with a hydraulic fluid, such as hydraulic oil, and a pressurized gas, usually compressed air, is adapted to be injected into the upper region of the chamber. The injection of the pressurized gas into the chamber 32 is accomplished through an inlet port 64, FIG. 4, to which a conventional hose fitting, not shown, is attached. The port 64 is in communication with a vertical passage 66 defined in the casing boss 68 which communicates with the uppermost region of the chamber adjacent the plate underside 14 through the outlet 70. In this manner, the pressurized 'gas introduced into the chamber 32 is introduced into the chamber upper portion and, as the chamber 32 is usually partially filled with a hydraulic liquid, no undesirable mixing of the air and fluid occurs.

Preferably, the expansible motor utilized with the jack is in the form of a flexible wall chamber device generally indicated at 72. The expansible motor illustrated includes an annular flexible wall 74 formed of rubber or the like closed at each end by a lower plate 76 and an upper plate 78. The end plates are each formed with a bead 80 receiving a formed and reinforced end of the flexible wall, and threaded insert caps 82 are attached to the end plates to permit attachment of the end plate 78 to the casing bottom wall 34, and the lower portion casing wall 84 may be attached to the plate 76. This type of expansible motor is available from several sources, such as that marketed by Firestone Industrial Products Company, identified as an Airstroke.

The pressurized medium is introduced into the expansible motor 72 through an orifice 86 defined in a threaded plug 88 located at the center of the upper motor plate 78. The orifice 86 communicates with a hole 90 defined in the chamber bottom wall 34, and communication is established between the interior of the motor 72 and the lower region of the reservoir chamber 32. Depending on how quickly it is desired to permit expansion of the jack, the plug 88 may be easily removed and replaced by another plug so that the diameter of the orifice 86 may be varied.

. A threaded plug 92 is formed in the frame plate 10 directly over the orifice 86 whereby inspection and access to the orifice plug is possible and bleeding of the chamber 32 facilitated.

In use, the expansible motor 72 is filled with a hydraulic liquid and the chamber 32 is charged with sufficient hydraulic fluid to exceed the amount of fluid required to fill motor 72 when fully extended. Thus, chamber 32 will be substantially filled with liquid when the jack is retracted as in FIG. 3.

A compressed air hose is attached to the inlet 64 by means of a quick disconnect coupling, or similar con ventional fitting, not shown, and the jack is positionted under the load to be lifted. Positioning of the jack is readily accomplished in that the support of the jack upon the ground wheels 16 permits the jack to be easily rolled across the floor or ground surface, and the tension springs 52 raise the casing lower portion 30 to its uppermost portion as shown in FIG. 3 wherein the abutment surfaces 94 on portion 30 engage the surface 96 on portion 28. In this relationship the casing bottom wall 84 is disposed close to, but slightly above, the surface of the floor as to not interfere with positioning of the jack as it is rolled about upon its caster wheels 16.

Once the jack is properly positioned under itsload, and it is desired to lift the load, compressed air is introduced into the upper regions of chamber 32 by means of passage 66. The presence of compressed air in the chamber 32 forces the hydraulic liquid therein through the orifice 86 pressurizing the fluid-within the expansible motor to expand and thereby force the lower casing portion 30 downwardly into engagement with the floor. As the pressure increases within the chamber 32 and the expansible motor 72, the frame plate 10 will be lifted, lifting the caster wheels from the floor and extension of the jack continues until the flange 40 engages the bolt heads 48. When used in handling boats, for instance, it is intended that four, or more, jacks of the type described be mounted under the boat cradle whereby lifting of the boat cradle at all locations may be simultaneously produced. In such an arrangement the compressed air supplying the jacks will be from a common source and thus an equalizing of the pressure within all of the jacks lifting the load is achieved.

Retraction of the jacks is produced by depressurizing the chamber 32. Depressurization of the chamber 32 permits the hydraulic liquid to flow from the pressurized motor 72 to the chamber 32 through the orifice 86. Such a flow of fluid from the pressurized motor to the chamber 32 is primarily produced by the weight of the object lifted and as soon as this weight has been removed from the jack by the wheels 16 engaging the floor, the biasing force imposed upon the casing portion 30 by the springs 52 will further force the hydraulic fluid from the expansible motor into the chamber and permit complete retraction of the jack to the position shown in FIG. 3.

In handling a boat, the retracted jacks constructed in accord with the invention are placed under a boat cradle prior to the boat being loaded on the cradle and when the boat is cradled the boat may be wheeled to the desired storage location on wheels 16. Once the storage location is achieved, the jacks are extended to lift the cradle and boat and blocks are inserted under the elevated cradle to permit retraction and removal of the jacks, which are then rolled to the next location of use.

Movement of the jack about on the floor is made easier if a handle is attachable to the plate and holes 98 are defined in the plate 10 for removably receiving a handle 100. A pair of holes 98 located near a common edge of plate 10 will permit the downwardly turned ends 102 of thehandle to be received therein to estab lish a firm connection between the handle and plate.

It will be appreciated that the previously described jack need "riot utilize a combination of compressed air and hydraulic liquid. For instance, even if no liquid is present in the chamber 32 and the expansible motor 72, the introduction of compressed air into the chamber will permit extension of the jack in the aforedescribed manner. However, by utilizing a combination of hydraulic liquid and air, the required volume of compressed air is substantially reduced.

FIG. 5 illustrates an embodiment of the invention wherein increased lifting capacity may be achieved in a jack having substantially the. same dimensions as the jack previously described.

In the embodiment of FIG. 5 the jack frame plate is shown at 104, and a plate 106 is affixed to the underside of the frame plate by means of bolts 108. A casing 110, of a generally cylindrical construction, is affixed to the underside of the plate 106 by the bolts W8, and includes a flange through which the bolts extend. The casing 110 includes an axially extending wall 112 and a bottom wall 114 wherein a chamber is defined therein.

The casing lower portion 116 is of a dished configuration including a bottom wall 118 and a circumferential flange 120. The bottom wall 114 and the bottom wall 118 define a chamber 122, and the casing lower portion 116 is biased toward the frame plate 10 i by a plurality of tension springs 124 evenly spaced about the periphery of the casing and each is anchored to the plate 106, and the flange 120 in the manner as the springs 52 of the embodiment of FIGS. ll through ll.

The casing upper portion bottom wall H4 is provided with a plurality of holes 126 which receive spacer sleeves 128. A plate 130 is mounted upon the upper end of the spacer sleeves 128, and bolts 13% extending through the casing lower portion flange, and the sleeves are threaded intothe plate 130. In this manner, the plate 130 is located within the casing upper portion chamber 134., and is rigidly connected to the casing lower portion lib.

An expansible motor 136 of the flexible wall type is located within the chamber 134' interposed between the plate ms and the plate in the manner previously described. Those components similar to those previously described are indicated by primes.

A second flexible expansible motor 133 is interposed between the casing bottom wall 114 and the casing lower portion bottom wall 118, and this expansible motor is of a slightly lesser diametrical dimension than expansible motor 136 with a casing of the configuration illustrated. However, by slight modifications of the configuration of the casing till, it is possible to use expansible motors of similar diametrical dimension.

A passage 140 is defined in the plate 106 and communicates with the interior of the expansible motor 136 through a hole 142 defined in the plate. Likewise, a passage 1144 is defined in the bottom wall 114 communicating with the interior of the expansible motor 138 through a hole 1146 defined in the motor upper plate. Passages 140 and 144 are preferably connected to a common compressed air supply source wherein both of the motors may be simultaneously pressurized.

Upon pressurization of the expansible motors .136 and HM the force exerted upon the plate 130 by expansible motor 13s, and the force exerted upon the casing bottom wall lllll by expansible motor 138 will produce the extension of the jaclt, and the lifting force. Upon depressurization of the expansible motors the springs l24 will lift the casing lower portion lid to the position shown in FIG. 5. Thus, it will be appreciated that the embodiment of FIG. 5 permits a substantially increased lifting capacity, as compared with the embodiment of FIGS. 1 through 4, in a jack having substantially the same basic dimensions as the previously described embodiment.

Another embodiment employing the inventive concepts is illustrated in FIGS. 6 and 7 wherein jack structure is also shown utilizing two flexible expansible motors connected in parallel such that an increased lifting capacity is achieved with respect to jacks utilizing a single expansible motor, however, this jacit construction is more economical and requires fewer specially formed components than the embodiment illustrated in FIG. 5.

FllG. 6 is a sectional view talten through a diameter of the illustrated assembly which intersects the studs maintaining the spacing of the movable assembly plates, and FllG. '7 is a diametrical sectional view revolved 45 about the assembly axis with respect to H6. h and taken through the passages drilled in the movable plates. l r

With reference to FIGS. 6 and 7, the wheeled portion of the jack is identical to that utilized with the previously described embodiments, and the illustrated as sembly structure is mounted to the underside lid of the plate lllll supported upon the ground wheels 16. A plate M8 is bolted to the underside of plate ll] by a plurality of bolts lfifl, one of which is shown inFIG. 6. The plate M8, as well as the other plates employed in this embodiment, may be of conventional steel sheet material readily available from many sources. i

Six shouldered bolts 152 threaded at their upperends into threaded holes defined in plate 148 extend downwardlyfrom the plate 148 and pass through holes defined in plate 154, whereby the plate R54 is maintained in spaced parallel relationship to plate 148 by the bolts. Nuts iss threaded upon the bolts M2 maintain the plate 154 against the bolt shoulders 158 to firmly position and fix the plate 154 relative to the plate 148.

Movable plates, directly associated with the expansible motors, as will be described, are guided for movement with respect to the plate 154. The intermediate plate 160 and the floor plate 162, which are of greater thickness than the plates 148 and 154, are maintained in spaced parallel relationship by six hexagonal studs 164 which include a maximum transverse dimension portion 166, a cylindrical guide portion 168, an upper threadedend portion 170, and a lower threaded end portion 172. The studs guide portion 168 is of a diameter less than that of the holes 174 defined in the plate 154 through which the portion 168 extends. The guide portion 168 defines a shoulder 176 with the portion 170, and this shoulder engages the lower side of the plate 160. Nut 178 holds the associated stud in firm engagement with the shoulder 176. The lower stud threaded ends 172 are threaded into threaded holes 180 defined in plate 162, and the longitudinal length of the hexagonal portions 166 determines the minimum spacing that can occur between plates 154-and 162. It will be appreciated that holes are formed in plate 160 to permit bolts 152 to pass therethrough.

A plurality of coil tension springs 182 are attached at their upper ends to the plate 148 and extend through clearance holes defined in plates 160 and 154 and are attached at their lower ends to the floor plate 162. The spring ends are preferably attached to their associated plates by a pin and hole arrangement such as described with respect to FIG. 3. The springs 182 impose an upward biasing force tending to raise the plate 162, and hence the plate 160, toward the frame 10. Such upward movement is limited by engagement of the stud shoulders 184 with the underside of the plate 154, as will be seen in FIG. 6.

The flexible wall expansible motors 186 and 188 are similar to those previously described and include combination insert caps and stops 190, which may be four in number with respect to each motor. As FIGS. 6 and 7 are diametrical sections only two caps 190 are visible in each view. The insert stops 190 provide a means for attaching the expansible motor head plates 192 and 194 to the associated plate by bolts, in a manner as will be apparent from FIGS. 3 and 5.

The lower head plates 194 of the expansible motors 186 and 188 are each provided with a central opening 196 which forms the access for the pressurized medium into the motors. With reference to FIG. 7, pressurized medium is introduced into motor 186 through a passage 198 defined in plate 160. The passage 198 is formed with a threaded inlet 200 to which a self-sealing coupling, not shown, is affixed. A flexible air hose will provide compressed air to the coupling. A standpipe 202 is mounted in the plate 160 extending through the opening 196 defined in the upper motor 186, and communicates at its lower end with the passage 198. The upper end of the standpipe 202 is disposed adjacent, but short of, the motor upper head plate 192 whereby the pressurized medium may flow through the standpipe into the expansible motor.

An outlet from the motor 186 is formed by the passage 204 communicating with the opening 196, and the passage 206 defined in the plate 160. The outer end of the passage 206 is sealed with a threaded plug 208.

Communication between the upper and lower expansible motors 186 and 188 is achieved by tube 210 sealingly connected at one end to the plate in communication with the passage 206, FIG. 7, and sealingly connected to the floor plate 162 by suitable sealing structure, including a resilient O-ring 212. Horizontally disposed passage 214 is defined in the floor plate 162 and communicates with the interior of motor 188 through its lower head plate opening 196 through vertical passage 216 intersecting passage 214. Also, plate 162 is formed with a bleed or filling passage 218 communicating with the interior of motor 188 through passage 220 and opening 196. The outer end of the passage 218 is normally closed by threaded plug 222.

The rate of flow of pressurized medium between the expansible motors is regulated by a plug valve 224 located in passage 214 mounted upon threaded plug 226. The diameter of the plug head 224 will determine the rate of flow through the passage 214, and if it is desired to change this rate of flow the size of plug head may be varied by replacing the existing plug with a plug of a different diameter.

The tube 210 passes through a clearance opening 228 defined in plate 154, and thus it will be appreciated that the fluid motors 186 and 188 will be in communication at all times. Preferably, the volume of the upper motor 186, when the apparatus is in the retracted or nonextended condition, is greater than the volume of the lower motor 188. This condition is shown in FIG. '7, and is achieved by predetermining the length of the stud portion 166, and the longitudinal distance between the stud shoulder 176 and the shoulder 184, FIG. 6. By making the volume of the upper motor 186 greater than that of the lower motor 188 the upper motor serves as a reservoir for the hydraulic liquid which preferably fills the motor 188, and substantially fills the motor 186. As previously described, the use of such hydraulic liquid substantially reduces the amount of compressed air required to permit expansion of the motors.

To fill the motors 186 and 188 with hydraulic liquid the jack apparatus may be inverted, and the bleeder plug 222 removed. Thereupon, hydraulic liquid is introduced into the motor 186 through the inlet 200 and passage 198 under pressure. In such instance the motor 186 will fill first, and upon the motor being filled the fluid will flow through the passages 204 and 206, tube 210 and passage 214 into the motor 188. When the motor 188 is filled this condition will be indicated by the flow of fluid from the bleeder passage 218, and the bleeder plug 222 is inserted to complete the filling procedure. The apparatus is then inverted to its normal position, and the motors will be substantially filled with hydraulic liquid. Upon the introduction of compressed air into the motor 186 through passage 198 a small amount of compressed air will exist immediately adjacent the upper head plate 192 of motor 186.

In use, the structure of FIGS. 6 and 7 will normally be in the retracted or raised" position shown in FIGS. 6 and 7. In this condition the lower surface of the floor plate 162 will be disposed above the floor surface so that the jack frame 10 may be freely wheeled upon its ground wheels 16. When it is desired to lift the frame 10 compressed air is introduced into the apparatus through inlet 200 causing a buildup of pressure within the motor 186, and simultaneously causing a buildup of pressure in the lower motor 188 due to the comm unication between the motors. As the motor 186 begins to expand it will force the plate 160 downwardly, and likewise the expansion of the motor 188 exerts a downward force on the floor plate 162. The hydraulic fluid will flow from the motor 186 into the motor 188 past the valve plug 224, and thus the valve 224 will regulate the rate at which the jack expands. Expansion of the motors continues until the plate 160 engages the fixed plate 154.

When it is desired to retract the jack structure in accord with the embodiment of FIGS. 6 and 7, the compressed air within the motor 186 is released through standpipe 202 and passage 198 by valve structure, not shown, associated with the compressed air supply, and as the compressed air within the upper portion of motor 186 exhausts from the motor the motors will simultaneously retract, initial retraction being primarily due to the weight of the load, and as soon as the ground wheels 16 engage the supporting floor, further retraction is due to the biasing force imposed by the springs 182. The motor structure will retract to the condition shown in FIGS. 6 and 7, which completes the cycle.

lt will therefore be appreciated that in the embodiment illustrated in FIGS. 6 and 7, the structure may be economically formed without requiring special castings and the like in that the various plates required need only be cut to the exact configuration, and drilled to provide the appropriate mounting and clearance holes, and the pressurized medium conducting passages may be readily drilled within plates 160 and 162. The formation of the studs 164 and the bolts 152 may be readily achieved with conventional machine tools, and as the fluid motors are of a readily available commercial construction the entire units may be economically produced.

As in the case with the embodiment shown in FIG. 5, the embodiment of H6. 6 and 7 permits twice the lifting force to be achieved that can be accomplished with a single expansible motor of the disclosed type, yet the space requirements for the apparatus substantially corresponds to that disclosed in the single motor embodiment of FIG. 3. i

As the jacks of the described embodiments will normally be used in sets, for instance, in handling a boat four or more jacks will be used depending on the boat size, it is possible to simultaneously raise all of the jacks by connecting the jacks to a common compressed air source through flexible hose and thus a uniform lifting on the boat cradle may be achieved. Such uniform lifting forces cannot be provided by the usual independently operated jacks that have been commonly used in the past.

it is appreciated that various modifications to the disclosed embodiments may be apparent to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

l. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixed to the underside of said frame, said assembly including an upper portion fixed relative to said frame and a lower portion guided upon and movable with respect to said upper portion in a direction toward and away from said frame, a chamber defined within said assembly upper portion comprising a fluid reservoir and having a bottom, expansible motor means supported upon said assembly interposed between said assembly upper and lower portions and operatively associated with said lower portion to position said lower portion with respect to said frame, a passage establishing communication between the lower portion of said chamber and said motor means, means for introducing a pressurized medium into said chamber, said motor means being filled with a liquid wherein introduction of the pressurized medium into said chamber pressurizes said motor means, for expanding said motor means and lowering said lower assembly portion into engagement with the jack supporting surface to raise said frame relative to the supporting surface.

2. In a portable jack as in claim 1 wherein said expansible motor means comprises a flexible wall chamber.

3. in a portable jack as in claim 1, wherein said assembly lower portion includes a peripheral flange, a plurality of springs disposed about said periphery of said lower portion, said springs each having a first end fixed relative to said frame and a second end connected to said flange whereby said springs bias said assembly lower portion toward said frame.

d. In a portable jack as in claim 1 wherein said motor means is located vertically below said chamber and said passage is defined in said chamber bottom.

s. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixedto the underside of said frame, said assembly including an upper portion fixed relative to said frame and a lower portion guided upon and movable with respect to said upper portion in a direction toward and away from said frame, expansible motor means comprising a pair of flexible wall chambers supported upon said assembly and operatively associated with said lower portion to position said lower portion with respect to said frame, means connecting said flexible wall chambers in parallel tosaid assembly lower portion comprising first and second bearing surfaces defined on said assembly upper portion and facing downwardly, said first bearing surface being located vertically above said second surface, first and secondbearing surfaces defined on said assembly lower portion facing upwardly, said first bearing surfaces and said second bearing surfaces of said assembly upper and lower portions, respectively, being in opposed spaced relationship, said flexible walled chambers comprising a first flexible wall expansible motor interposed between said first bearing surfaces, and a second flexible wall expansible motor interposed between said second bearing surfaces wherein expansion of both chambers translates said assembly lower portion away from said frame, means for introducing said pressurized medium into said motor means including passages communicating with each chamber and with each other for expanding said flexible wall chambers and lowering said lower assembly portion into engagement with the jack supporting surface to raise said frame relative to the supporting surface.

6. In a portable jack as in claim 5, conduit passage means extending between said first and second expansible motors establishing communication between said motors, said means for introducing pressurized medium into said motor means communicating with said first expansible motor whereby pressurized medium during pressurizing flows through said first motor to said second motor.

7. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixed to the underside of said frame, said assembly including an upper plate fixed relative to said frame underside and a lower plate disposed below said upper plate in fixed, spaced, parallel relation thereto, an intermediate plate located between said upper and lower plates movable in a vertical-direction therebetween, a floor plate disposed vertically below said lower plate in spaced, parallel relation to and fixed to said intermediate plate for movement therewith, a first flexible wall expansible motor interposed between said upper and intermediate plates, a second flexible wall expansible motor interposed between said lower and floor plates, conduit means interconnecting said first and second motors, and means for introducing pressurized medium into said first motor.

8. In a portable jack as in claim 7 wherein said conduit means includes a first passage defined in said intermediate plate communicating with said first motor, a second passage defined in said floor plate communicating with said second motor, and a tubular conduit extending between said intermediate and floor plates communicating with said first and second passages.

9. In a portable jack as in claim 8 wherein said means for introducing pressurized medium into said first motor includes a standpipe having an upper end communicating with the upper region of said first motor, said first passage communicating with the lower region of said first motor, and said second passage communieating with the lower region of said second motor.

10. In a portable jack as in claim 8, fluid flow control means located within said conduit means controlling the rate of flow of fluid between said first and second motors.

* x a: a: 

1. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixed to the underside of said frame, said assembly including an upper portion fixed relative to said frame and a lower portion guided upon and movable with respect to said upper portion in a direction toward and away from said frame, a chamber defined within said assembly upper portion comprising a fluid reservoir and having a bottom, expansible motor means supported upon said assembly interposed between Said assembly upper and lower portions and operatively associated with said lower portion to position said lower portion with respect to said frame, a passage establishing communication between the lower portion of said chamber and said motor means, means for introducing a pressurized medium into said chamber, said motor means being filled with a liquid wherein introduction of the pressurized medium into said chamber pressurizes said motor means, for expanding said motor means and lowering said lower assembly portion into engagement with the jack supporting surface to raise said frame relative to the supporting surface.
 2. In a portable jack as in claim 1 wherein said expansible motor means comprises a flexible wall chamber.
 3. In a portable jack as in claim 1, wherein said assembly lower portion includes a peripheral flange, a plurality of springs disposed about said periphery of said lower portion, said springs each having a first end fixed relative to said frame and a second end connected to said flange whereby said springs bias said assembly lower portion toward said frame.
 4. In a portable jack as in claim 1 wherein said motor means is located vertically below said chamber and said passage is defined in said chamber bottom.
 5. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixed to the underside of said frame, said assembly including an upper portion fixed relative to said frame and a lower portion guided upon and movable with respect to said upper portion in a direction toward and away from said frame, expansible motor means comprising a pair of flexible wall chambers supported upon said assembly and operatively associated with said lower portion to position said lower portion with respect to said frame, means connecting said flexible wall chambers in parallel to said assembly lower portion comprising first and second bearing surfaces defined on said assembly upper portion and facing downwardly, said first bearing surface being located vertically above said second surface, first and second bearing surfaces defined on said assembly lower portion facing upwardly, said first bearing surfaces and said second bearing surfaces of said assembly upper and lower portions, respectively, being in opposed spaced relationship, said flexible walled chambers comprising a first flexible wall expansible motor interposed between said first bearing surfaces, and a second flexible wall expansible motor interposed between said second bearing surfaces wherein expansion of both chambers translates said assembly lower portion away from said frame, means for introducing said pressurized medium into said motor means including passages communicating with each chamber and with each other for expanding said flexible wall chambers and lowering said lower assembly portion into engagement with the jack supporting surface to raise said frame relative to the supporting surface.
 6. In a portable jack as in claim 5, conduit passage means extending between said first and second expansible motors establishing communication between said motors, said means for introducing pressurized medium into said motor means communicating with said first expansible motor whereby pressurized medium during pressurizing flows through said first motor to said second motor.
 7. A portable jack comprising, in combination, a frame having an upper side and an under side, a plurality of ground wheels mounted upon the underside of said frame for supporting said frame in spaced relation to the jack supporting surface, an expansible motor assembly affixed to the underside of said frame, said assembly including an upper plate fixed relative to said frame underside and a lower plate disposed below said upper plate in fixed, spaced, parallel relation thereto, an intermediate plate located between saiD upper and lower plates movable in a vertical direction therebetween, a floor plate disposed vertically below said lower plate in spaced, parallel relation to and fixed to said intermediate plate for movement therewith, a first flexible wall expansible motor interposed between said upper and intermediate plates, a second flexible wall expansible motor interposed between said lower and floor plates, conduit means interconnecting said first and second motors, and means for introducing pressurized medium into said first motor.
 8. In a portable jack as in claim 7 wherein said conduit means includes a first passage defined in said intermediate plate communicating with said first motor, a second passage defined in said floor plate communicating with said second motor, and a tubular conduit extending between said intermediate and floor plates communicating with said first and second passages.
 9. In a portable jack as in claim 8 wherein said means for introducing pressurized medium into said first motor includes a standpipe having an upper end communicating with the upper region of said first motor, said first passage communicating with the lower region of said first motor, and said second passage communicating with the lower region of said second motor.
 10. In a portable jack as in claim 8, fluid flow control means located within said conduit means controlling the rate of flow of fluid between said first and second motors. 